Stretching and bending normal vibrations of AB2(C2v), AB3(D3h), AB4(D4h), and AB5(D3h) molecules are described by correlating the vibrational displacement vectors of the attached atoms with the standard representations of s, p and d atomic orbitals of the central atom in ABn(n=2-5) molecules. It is found that stretching and bending normal vibrations of simple molecules accord with probability density of hybrid orbitals of the central atom. So, stretching and bending normal vibrations can be determined based on the irreducible representations of each vibration, and symbols for the representations which are suggested by Muliken.